Hydroxyethyl starch has routinely been used as a sedimenting agent [Lionetti, U.S. Pat. No. 4,004,975; Pestka, U.S. Pat. No. 4,289,690; Djerassi, U.S. Pat. No. 4,111,199; Chadha, U.S. Pat. No. 4,485,038; and Van Oss, et al., Immunol. Commun., 10(6), pp. 549-55 (1981)]. Treatment with hydroxyethyl starch ("HES") results in recovery of about 68% of the original pool of leukocytes or white blood cells ("WBC"). Ammonium chloride lysis yields 90% of the WBCs, but is undesirable in view of the wasteful destruction of the red blood cells ("RBCs").
Other agents which have been used as sedimenting agents are Dextran (glucose polymer), Ficoll (sucrose polymer), PVP, fenugreek seed extract, and phytohemagglutinins [Lichtenstein, U.S. Pat. No. 3,709,791; Chany, U.S. Pat. No. 3,560,611; Ferrante, U.S. Pat. No. 4,255,256; Guirgis, U.S. Pat. No. 4,152,208; Furuta, U.S. Pat. No. 4,409,106; Goore, U.S. Pat. No. 3,800,035; Shepherd, U.S. Pat. No. 3,594,276; Kirkham, U.S. Pat. No. 3,635,798; Widmark, U.S. Pat. No. 3,700,555].
Kanter, U.S. Pat. No. 4,487,700, refers to athixotropic barrier material of intermediate density to separate lymphocytes from erythrocytes and phagocytized leukocytes. Meyst, U.S. Pat. No. 4,283,289 refers to a leukocyte filter. The use of NH.sub.4 Cl to lyse RBCs, while leaving most WBCs intact, is also known.
Hydroxyalkyl celluloses, and particularly hydroxyethyl cellulose, have been used as a thickening and stabilizing agent in pharmaceuticals and other compositions. However, they have never been used as sedimenting agents to separate lymphocytes from erythrocytes.